The present invention relates generally to the field of fuel cell systems and more particularly to operation of fuel cell systems to allow for efficient, extended-life operation with decreased anode leading edge damage and carbon deposition.
Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide reversible fuel cells, that also allow reversed operation, such that water or other oxidized fuel can be reduced to unoxidized fuel using electrical energy as an input.
In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing gas is passed through the cathode side of the fuel cell while a fuel flow is passed through the anode side of the fuel cell. The oxidizing gas is typically air, while the fuel flow is typically a hydrogen-rich gas created by reforming a hydrocarbon fuel source. Water may also be introduced into the system in the form of steam. The fuel cell, typically operating at a temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ions combine with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ions are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit.